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Nitrogen-fixing nodules on lupin root
Nitrogen-fixing nodule. Macrophotograph of a section through a nitrogen-fixing nodule on the root of a lupin (Lupinus polyphyllus). The nodule contains Rhizobium leguminosarum bacteria. These take nitrogen gas from the air and bind it up in compounds which the plant can use for its nutrit- ion. They do this using an iron-containing protein called leghaemoglobin, similar to the haemoglobin found in red blood cells. It is responsible for the pink colour seen here. The plants benefit from this symbiosis as it means they can grow in soils with a low nitrogen content, which are inaccessible to other plants. Magnification: x2 at 35mm size.
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